Error with clickedEvent, but why?

Hello! i have line where i call clickedEvent, and it not working and gives an error: Error running Lua task: [A5C88492F19F2E34] MainUIScript:27: attempt to call a sol.sol::detail::unique_usertype<FScriptEvent> value (field 'clickedEvent')
I tryed call function UI.SetCanCursorInteractWithUI(true), but this isn't helped with this error.
Here's my script:

-- MainUIScript
-- By Hramzhuk

-- define variables

local mainUI = World.FindObjectByName("MainUI")
local mainMenuContainer = mainUI:FindChildByName("MainMenuContainer")
local gameOverMenuContainer = mainUI:FindChildByName("GameOverMenuContainer")
local playButton = mainMenuContainer:FindChildByName("PlayButton")
local backToMainMenuButton = gameOverMenuContainer:FindChildByName("BackToMainMenuButton")


-- set all needed for player to enable him press buttons


-- define button functions

function playButtonClicked()
	print("Button clicked!")

-- set button functions on certain events


Update! That was my carelessness, and error was that i don't typed :Connect after clickedEvent.